JP2001267841A - Antenna system and portable radio equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an antenna system which has simple device structure and can be used at a plurality of comparatively close frequency bands. SOLUTION: Phase shifting circuits 13, 14 for changing the phase of a radio wave so as to obtain high impedance when one antenna element is used at the resonance frequency of the other antenna element are respectively connected between the feeding points of the two antenna elements 11, 12 having respectively different resonance frequency bands and a radio circuit 16.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antenna device for transmitting or receiving radio waves of two or more frequencies, and more particularly, to an antenna device which can be mounted on a portable radio device such as a portable telephone. This portable radio is related.

[0002]

2. Description of the Related Art In recent years, portable telephones have rapidly become widespread. In portable telephones, there is an increasing demand for a wider frequency band to be used in order to increase transmission efficiency and prevent noise and interference. However, since the antenna structure of the conventional mobile phone cannot cover a wide frequency band, development of a method of mounting an antenna that can be used at a plurality of frequencies and realizing transmission and reception in a wider band has been advanced.

FIGS. 18 and 19 show examples of conventional antennas usable in a plurality of frequency bands. FIG. 18 shows an example in which a parasitic element is used, and FIG. 19 shows an example in which a plurality of radiation conductors are used.

In an antenna 180 shown in FIG. 18, a dielectric substrate 182 is connected to a coaxial cable 181 which is a transmission line, and a radiation conductor 183 and a parasitic element 184 are arranged close to the dielectric substrate 182. It is often used as a method for obtaining multiple resonance characteristics. In the antenna 190 shown in FIG. 19, the substrate 1 is used without using the parasitic element 184.
A plurality of radiation conductors 19 having different resonance frequencies on 91
The double resonance characteristics are obtained by arranging 2 and 193 side by side and feeding power from one feeding point 194. The antenna 190
Are grounded at the ground point 195.

[0005]

In the antenna 180 in which the parasitic element is arranged as shown in FIG.
Since the positional relationship between the antenna and the radiating element 193 has a great influence on the impedance characteristics of the antenna, it is problematic that an arbitrary antenna cannot be arranged.

Further, even in the antenna 190 shown in FIG. 19 where no parasitic element is disposed, a large accommodation space is required because the radiation conductors 192 and 193 resonating in a plurality of frequency bands are arranged. Furthermore, this type of antenna has a problem that it is generally difficult to operate when the operating frequencies of the antennas are close to each other within a range of about 10%. This is because in a configuration such as the antenna 190, the radiation conductors 192 and 193 of the antenna are separated by slits and operated at their respective resonance frequencies to realize multiple resonance.
This is because each of the radiation conductors 192 and 193 has a certain broadband property, and when the frequencies are close to each other, the antennas are not separated by a slit, so that multiple resonance cannot be obtained. However, the above-mentioned portable telephone needs to be usable at a close frequency.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide an antenna device which can be used at a plurality of relatively close frequencies with a simple configuration. It is another object of the present invention to provide a portable wireless device which can be used with a plurality of relatively close frequencies with a simple configuration.

[0008]

According to the present invention, in order to solve the above-mentioned problems, in an antenna apparatus for transmitting or receiving radio waves of two frequencies, feed points of two antenna elements having different resonance frequencies are respectively set to a phase difference. The antenna device is connected to a wireless circuit via two phase shift circuits for changing the phase shift.

In such an antenna device, by connecting the antenna element to the feeding point via the phase shift circuit, the impedance characteristic of the other adjacent antenna element at the resonance frequency is adjusted to eliminate the influence between the antennas. Thus, it is possible to use the device at different frequencies relatively close to each other with a simple configuration.

Further, according to the present invention, in a portable wireless device for transmitting or receiving radio waves of a plurality of frequencies, the feeding points of two antenna elements having different resonance frequencies are respectively connected via two phase shift circuits for changing phases. And a portable wireless device equipped with an antenna device that is connected to a wireless circuit.

In such a portable wireless device, in the mounted antenna device, the antenna element is connected to the feeding point via the phase shift circuit, so that the impedance characteristic at the resonance frequency of another adjacent antenna element is reduced. The adjustment is performed to remove the influence between the antennas, and it becomes possible to transmit or receive radio waves of different frequencies relatively close to each other with a simple device configuration.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. In the following description, unless otherwise specified, the description will be made with respect to the time of transmission of radio waves. it is obvious.

FIG. 1 shows a main configuration of an antenna device according to the present invention. The antenna device 1 transmits radio waves of two wavelengths by two antenna elements having different resonance frequencies, and is mainly used by being mounted on a portable wireless device such as a mobile phone. Applicable to

In the antenna apparatus 1, two antenna elements 11 and 12 having different resonance frequencies are connected to phase shift circuits 13 and 14 at respective feeding points, and an oscillator 15 for generating radio waves of two predetermined wavelengths is provided. And the phase shift circuits 13 and 14 are connected. The power generated by the oscillator 15 is simply split,
After being distributed, they are supplied to antenna elements 11 and 12 via phase shift circuits 13 and 14, respectively. Phase shift circuit 1
Reference numerals 3 and 14 are composed of lumped constant circuits or distributed constant circuits.

Here, assuming that the resonance frequency of the antenna element 11 is f1 and the resonance frequency of the antenna element 12 is f2,
The phase shift circuit 13 changes the phase of the radio wave of the resonance frequency f2, and the phase shift circuit 14 changes the phase of the radio wave of the resonance frequency f1 by a predetermined amount. That is, the antenna elements 11 and 12 are matched at their own resonance frequencies f1 and f2, and the phase shift circuits 13 and 14 are connected to the other resonance frequencies f2 and f1 respectively.
The phase is changed by a predetermined amount experimentally determined so as not to operate when the radio wave is supplied.

The setting of the amount of phase change will be described with reference to a Smith chart. FIG. 2 is a Smith chart showing an example of input impedance characteristics of the antenna element 11,
(A) shows a case where the phase shift circuit 13 is not connected, and (b) shows a case where the phase shift circuit 13 is connected. FIGS. 3A and 3B are Smith charts showing an example of the input impedance characteristic of the antenna element 12, wherein FIG. 3A shows the case where the phase shift circuit 14 is not connected, and FIG. 3B shows the case where the phase shift circuit 14 is connected.

In these Smith charts, for the normalized impedance obtained by normalizing the input impedance by the characteristic impedance 50 Ω of the circuit, the real part is represented by, for example, a resistance line 21 in FIG. ing. In these Smith charts, the input impedance characteristic when the frequency of the input wave is changed is represented by the circular locus shown in the figure, and the record when the frequency is increased clockwise is shown. Have been.

The input impedance characteristic of the antenna element 11 alone is almost at the center of the chart at the resonance frequency f1 indicated by the arrow in FIG. FIG. 2B shows a state in which the phase shift circuit 13 has changed the phase from the antenna element 11 by the phase change amount dφ1.
In the chart, the position of f2 is represented by being rotated by the phase change amount dφ1 without changing the position of f1.
That is, in FIG. 2B, the input impedance at f2 is sufficiently higher than that at f1 while the matching at the frequency of f1 is maintained by the phase shift circuit 13; It can be seen that the phase change amount dφ1 is set so that the antenna element 11 does not operate at f2.

Similarly, in FIG.
Is matched at the resonance frequency f2 of FIG.
In (b), the position of f1 is represented by being rotated by the amount of phase change dφ2 without changing the position of f2 on the chart, and the phase shift circuit 14 maintains the matching when the frequency of the incident wave is f2. It can be seen that the phase change amount dφ2 is set so that the input impedance at f1 is sufficiently high.

As described above, the input impedance at the resonance frequency of the other adjacent antenna element becomes sufficiently large due to the phase change by the phase shift circuit, so that the mutual influence of the operating frequency of the antenna element can be made very small. Thus, an antenna device capable of operating at two frequencies can be realized with a simple structure in which both antenna elements are connected in parallel.

Next, an example of a phase shift circuit used in the antenna device 1 will be described. 4 and 5 show examples of a phase shift circuit constituted by a lumped constant circuit. Fig. 4 is + (positive)
Is a phase shift circuit that realizes the phase change amount of FIG.
This is a phase shift circuit that realizes a (negative) phase change amount. Also,
FIGS. 6, 7 and 8 show examples of the phase shift circuit constituted by the distributed constant circuit. 6 is a coaxial line, and FIG.
FIG. 8 shows a microstrip line.

As an example of a phase shift circuit using a lumped constant circuit,
In FIG. 4, an inductor 41 is connected in series, and capacitors 42 and 43 are connected in parallel. Here, considering the change of the phase shift in the Smith chart of FIG. 2A, when the inductor 41 is inserted in series, the locus of the impedance characteristic moves clockwise along the resistance line 21. Also, the resistance line 2 on the chart
Considering a conductance line (not shown) which is drawn symmetrically to 1 (immittance chart), when the capacitors 42 and 43 are inserted in parallel, the locus moves clockwise along the conductance line. That is, it can be seen that the phase of the incident wave is moved in the positive direction by this phase shift circuit.

In FIG. 5, a capacitor 51 is connected in series, and inductors 52 and 53 are connected in parallel. Similarly, considering the Smith chart, when the capacitor 51 is inserted in series, the locus moves counterclockwise along the resistance line 21. When the inductors 52 and 53 are inserted in parallel, the trajectory moves counterclockwise along the conductance line. That is, it can be seen that the phase of the incident wave is moving in the negative direction by this phase shift circuit.

On the other hand, as the distributed constant circuit used as the phase shift circuit, the coaxial line shown in FIG. 6, the two parallel lines shown in FIG. 7, and the microstrip line shown in FIG. 8 can be applied. The coaxial line shown in FIG. 6 includes an inner conductor 61, an outer conductor (not shown), and a dielectric 62 supporting the outer conductor. Generally, the outer conductor is a braided wire, the inner conductor 61 is a single wire or a stranded wire,
The dielectric 62 is filled with polyethylene or the like. The parallel two lines shown in FIG. 7 are generally used for transmitting and receiving short-wave bands and as a power supply line for a television. The structure is simple and the cost is low. Inductive interference and radiation loss are extremely large as compared with. Further, the microstrip line shown in FIG.
A dielectric 82 and a conductor 83 are formed on 1.

FIGS. 6, 7 and 8 show equations for calculating the phase change amount dφ after passing through the respective circuits. In these distributed constant circuits, as shown in these equations, the transmission line through which signals pass is shown. Is changed by changing the physical length L of the signal. In each transmission line, the relationship between the physical length of the circuit and the electrical length in the circuit differs depending on the thickness and thickness of the conductor, the relative permittivity εr of the dielectric, etc.
The effect of the phase change can be obtained by using any circuit. However, from the structural advantage that it can be mounted on a substrate and the low manufacturing cost, a microstrip line is considered to be the most suitable as a phase shift circuit when used in a portable wireless device.

Next, FIGS. 9 and 10 show examples of calculated values obtained by circuit simulation for the total impedance characteristics of the antenna elements 11 and 12, respectively, and FIGS. 11 and 12 show the return loss characteristics. . 9 shows the input impedance characteristics when the phase shift circuits 13 and 14 are connected, FIG. 10 shows the input impedance characteristics when the phase shift circuits 13 and 14 are not connected, and FIG. 11 shows the input impedance characteristics when the phase shift circuits 13 and 14 are connected. Case 1
Reference numeral 2 denotes a return loss characteristic when the phase shift circuits 13 and 14 are not connected.

FIGS. 9, 10, 11 and 12
In the simulation in which the value of was obtained, a distributed constant circuit was used as the phase shift circuit, and the frequency was changed from 1 GHz to 3 GHz.
The characteristics when changed up to are recorded. The resonance frequencies f1 and f2 of the antenna elements 11 and 12 are 1.95 GHz and 2.14 GHz, respectively, and the measurement points at these frequencies are indicated by M1 and M2 in the figure, respectively. The measured values of the input impedance of M2 are Z1 and Z2, and the measured values of the return loss are RL1 and RL2.
Are indicated by.

In FIG. 9, when the frequencies are f1 and f2, they are almost at the center of the chart, and at this frequency, they are almost matched. In FIG. 11, the loss is clearly seen in portions other than f1 and f2. Is getting higher. However, FIG. 10 shows a state in which matching at the operating frequency is not achieved, and FIG.
Then, the loss at the operating frequency is large. Therefore, the influence between the antenna elements is suppressed by the connection of the phase shift circuits 13 and 14, and good two-frequency operation characteristics are obtained. As described above, the antenna device 1 has a favorable operation characteristic for use at two adjacent frequencies, although it has a simple device configuration. In addition, the same device configuration separates
Naturally, it is also possible to operate by selecting one frequency.

In the above antenna device 1, the phase change amount changed by the phase shift circuit is set to nλ / 2 (where λ is the wavelength of the wave used by the adjacent antenna element, and n is an integer). ) Can theoretically perform the same operation as described above theoretically from the nature of the antenna. This is illustrated, for example, in FIGS. 2 (b) and 3 (b).
Then, the scale of the outer circle of the Smith chart is 0.
5, which is clear from the fact that even if the measurement line in the figure is rotated once, the position becomes the same as that in the original figure. However, in an actual circuit, the loss increases as | n | increases, which causes a problem that the usable frequency band decreases. Therefore, it is desirable to reduce n as much as possible.

In the above description, an antenna device using two antenna elements has been described. Similarly, two or more antenna elements are used to similarly connect an antenna element connected to a phase shift circuit to a radio circuit. By connecting, an antenna device which can operate at a plurality of frequencies can be realized. The number of frequencies that can be operated by such an antenna device 1 is determined by the frequency characteristics of the antenna element and the frequency characteristics of the phase shift circuit, and there is essentially no limit to the number of operating frequencies. However, in practice, the operation at about four frequencies can be the upper limit. For example, in such an antenna device, in one antenna element, the target frequency of the phase shift circuit connected thereto is different from that of another antenna element. One of the operating frequencies is selected. At other operating frequencies of the antenna element, good impedance characteristics are not always obtained, and the operable frequency itself may be limited.

Next, FIGS. 13, 14, 15, 16 and 17 show examples of antenna elements applicable to the antenna device of the present invention. 13 shows a dipole antenna, FIG. 14 shows a loop antenna, FIG. 15 shows a plate-shaped inverted F antenna, FIG. 16 shows an inverted L antenna, and FIG. 17 shows a helical antenna.

In the example using the dipole antenna of FIG. 13, if the wavelength of the resonance wave is λ, the dipole antenna 1
The lengths of 31 and 132 are usually selected to be λ / 2, but if the antenna length is shorter than this, matching may not be achieved. And 18 are connected. The radio circuit 16 is usually an unbalanced circuit in which one end of the circuit is grounded, and the dipole antenna is a balanced antenna.
If these are directly connected, an unbalanced current will flow and power loss will occur, so a balanced-unbalanced conversion circuit (Balun: a balance
to unbalance transformer) 19 is required. This type of dipole antenna, a tip-feed type whip antenna, is generally used for in-vehicle and portable wireless devices, and is suitable as an antenna element when the antenna device of the present invention is mounted on these devices. is there.

In the loop antennas 141 and 142 shown in FIG. 14, the diameter is usually selected to be one wavelength or less. If the diameter is less than one wavelength, each antenna element and the phase shift circuits 13 and 14 are used.
And matching circuits 17 and 18 are connected. Since the loop antenna is a balanced antenna, the radio circuit 16
And the connection of the balance-unbalance conversion circuit 19 is required.

The plate-shaped inverted-F antennas 151 and 152 shown in FIG. 15 are unbalanced antennas, so that a balanced-unbalanced conversion circuit is not required, and the radio circuit 16 and the phase shift circuits 13 and 1 are not required.
4 can be directly connected and matching can be performed by the antenna itself, so that there is no need to connect a matching circuit. The plate-shaped inverted-F antenna and an antenna element using the same are used as a built-in antenna for a mobile phone or the like, and are suitable as an antenna element when the antenna device of the present invention is mounted on a mobile phone.

The inverted L antennas 161 and 162 shown in FIG. 16 are unbalanced antenna elements, and have a structure in which a monopole antenna is bent to lower the attitude. Requires a connection.

The helical antennas 171 and 172 shown in FIG. 17 are unbalanced spiral antenna elements.
Depending on the diameter and length of the helix, it may be used as a directional antenna or a horizontal omnidirectional antenna. Normally, matching circuits 17 and 1 are provided between phase shift circuits 13 and 14.
8 is connected.

[0037]

As described above, in the antenna device of the present invention, the impedance characteristic at the resonance frequency of another adjacent antenna element is adjusted by connecting the antenna element to the feeding point via the phase shift circuit. This eliminates the effects between antennas and allows for use at different frequencies relatively close together with a simple configuration.

In the portable wireless device of the present invention, in the mounted antenna device, the antenna element is connected to the feeding point via the phase shift circuit, so that the impedance at the resonance frequency of another adjacent antenna element is obtained. The characteristics are adjusted to eliminate the influence between the antennas, so that it is possible to transmit or receive radio waves of different frequencies relatively close to each other with a simple device configuration.

[Brief description of the drawings]

FIG. 1 is a diagram showing a main configuration of an antenna device of the present invention.

FIG. 2 is a Smith chart showing an example of input impedance characteristics of an antenna element having a resonance frequency of f1, where (a) shows a case where a phase shift circuit is not connected, and (b) shows a case where a phase shift circuit is connected.

3A and 3B are Smith charts illustrating an example of input impedance characteristics of an antenna element having a resonance frequency of f2, where FIG. 3A illustrates a case where a phase shift circuit is not connected, and FIG. 3B illustrates a case where a phase shift circuit is connected.

FIG. 4 is an example of a phase shift circuit configured by a lumped constant circuit, and is a diagram illustrating a phase shift circuit that realizes a positive phase change amount.

FIG. 5 is an example of a phase shift circuit configured by a lumped constant circuit, and is a diagram illustrating a phase shift circuit that realizes a negative phase change amount.

FIG. 6 is a diagram illustrating an example of a phase shift circuit configured by a distributed constant circuit, illustrating a coaxial line.

FIG. 7 is an example of a phase shift circuit configured by a distributed constant circuit, showing two parallel lines.

FIG. 8 is an example of a phase shift circuit configured by a distributed constant circuit, and is a diagram illustrating a microstrip line.

FIG. 9 is a Smith chart showing input impedance characteristics when a phase shift circuit is connected.

FIG. 10 is a Smith chart showing input impedance characteristics when a phase shift circuit is not connected.

FIG. 11 is a diagram illustrating return loss characteristics when a phase shift circuit is connected.

FIG. 12 is a diagram illustrating return loss characteristics when a phase shift circuit is not connected.

FIG. 13 is a diagram showing a dipole antenna which is an example of an antenna element applicable to the antenna device of the present invention.

FIG. 14 is a diagram showing a loop antenna which is an example of an antenna element applicable to the antenna device of the present invention.

FIG. 15 is a diagram showing a plate-shaped inverted-F antenna which is an example of an antenna element applicable to the antenna device of the present invention.

FIG. 16 is a diagram showing an inverted L antenna which is an example of an antenna element applicable to the antenna device of the present invention.

FIG. 17 is a diagram showing a helical antenna which is an example of an antenna element applicable to the antenna device of the present invention.

FIG. 18 is a diagram illustrating an example of an antenna using a parasitic element that can be used at a plurality of frequencies.

FIG. 19 is a diagram showing an example of an antenna using a plurality of radiation conductors usable at a plurality of frequencies.

[Explanation of symbols]

1 ... antenna device, 11, 12 ... antenna element, 1
3, 14 phase shift circuit, 15 oscillator, 16 wireless circuit

Claims (12)

[Claims] 1. An antenna device for transmitting or receiving radio waves of two frequencies, wherein feed points of two antenna elements having different resonance frequencies are respectively connected to a radio circuit via two phase shift circuits for changing phases. An antenna device characterized by being performed. 2. The phase shift circuit changes the phase of this radio wave so that each of the connected antenna elements has a high impedance when used at the resonance frequency of the other antenna element. The antenna device according to claim 1, wherein: 3. The antenna device according to claim 1, wherein said phase shift circuit is constituted by a lumped constant circuit. 4. The antenna device according to claim 1, wherein said phase shift circuit is constituted by a distributed constant circuit. 5. An antenna apparatus for transmitting or receiving radio waves of a plurality of frequencies, wherein feed points of a plurality of antenna elements having different resonance frequencies are respectively connected to a radio circuit via a plurality of phase shift circuits for changing phases. An antenna device characterized by being performed. 6. The phase shift circuit changes the phase of the radio wave so that each of the connected antenna elements has a high impedance when used at the resonance frequency of another antenna element. The antenna device according to claim 5, wherein: 7. The antenna device according to claim 5, wherein said phase shift circuit is constituted by a lumped constant circuit. 8. The antenna device according to claim 5, wherein said phase shift circuit is constituted by a distributed constant circuit. 9. In a portable wireless device for transmitting or receiving radio waves of a plurality of frequencies, feed points of two antenna elements having different resonance frequencies are respectively connected to a wireless circuit via two phase shift circuits for changing phases. A portable wireless device equipped with an antenna device to be connected. 10. The portable wireless device according to claim 9, wherein said portable wireless device is a portable telephone. 11. A portable wireless device for transmitting or receiving radio waves of a plurality of frequencies, wherein feed points of a plurality of antenna elements having different resonance frequencies are respectively connected to a wireless circuit via a plurality of phase shift circuits for changing phases. A portable wireless device equipped with an antenna device to be connected. 12. The portable wireless device according to claim 11, wherein said portable wireless device is a portable telephone.